1. Field of the Invention
The present invention relates to a novel compound useful as a photoelectric conversion device material, a film containing the material, a photoelectric conversion device, a production method thereof, a photosensor, an imaging device and their use methods.
2. Description of the Related Art
Conventional photosensors in general are a device fabricated by forming a photodiode (PD) in a semiconductor substrate such as silicon (Si). As for the solid-state imaging device, there is widely used a flat solid-state imaging device where PD are two-dimensionally arrayed in a semiconductor substrate and a signal according to a signal charge generated by photoelectric conversion in each PD is read out through a CCD or CMOS circuit.
The method for realizing a color solid-state imaging device is generally fabrication of a structure where on the light incident surface side of the flat solid-state imaging device, a color filter transmitting only light at a specific wavelength is disposed for color separation. In particular, a single-plate solid-state imaging device in which color filters transmitting blue (B) light, green (G) light and red (R) light, respectively, are regularly disposed on each of two-dimensionally arrayed PD is well known as a system widely used at present in a digital camera and the like.
In this single-plate solid-state imaging device, since the color filter transmits only light at a limited wavelength, light failed in transmitting through the color filter is not utilized and the light utilization efficiency is bad. Also, in recent years, fabrication of a multipixel device is proceeding, and the pixel size and in turn, the area of a photodiode part become small, which brings about problems of reduction in the aperture ratio and reduction in the light collection efficiency.
In order to solve these problems, a system of stacking, in the longitudinal direction, photoelectric conversion parts capable of detecting light at different wavelengths has been proposed. As regards such a system, in so far as visible light is concerned, there are disclosed, for example, a system utilizing wavelength dependency of the absorption coefficient of Si, where a vertical stack structure is formed and colors are separated by the difference in the depth (Patent Document 1), and a system where a first light-receiving part using an organic semiconductor and second and third light-receiving parts each composed of Si are formed (Patent Document 2).
However, such a system is disadvantageous in that the color separation is poor, because the absorption range is overlapped among respective portions in the depth direction of Si and the spectroscopic property is bad. As for other methods to solve the problems, a structure where a photoelectric conversion film by amorphous silicon or an organic photoelectric conversion film is formed on a signal reading substrate, is known as a technique for increasing the aperture ratio.
Also, several examples are known for a photoelectric conversion device, an imaging device, a photosensor and a solar cell each using an organic photoelectric conversion film. The photoelectric conversion device using an organic photoelectric conversion film faces the task in particular of increasing the photoelectric conversion efficiency and decreasing the dark current, and as a method for improving these, there are disclosed, for example, introduction of a pn-junction or introduction of a bulk heterojunction structure for the former and introduction of a blocking layer for the latter.
In an attempt to increase the photoelectric conversion efficiency by the introduction of pn-junction or bulk heterojunction structure, an increase in the dark current often becomes a problem. Also, the degree of improvement in the photoelectric conversion efficiency differs depending on the combination of materials and in some cases, the ratio of photosignal amount/dark time noise does not increase from that before introduction of the structure above. In the case of employing the method above, what materials are combined is important and in particular, when reduction in the dark time noise is intended, this is difficult to achieve by conventionally reported combinations of materials.
Furthermore, the kind of the material used and the film structure are not only one of main factors for the photoelectric conversion efficiency (exciton dissociation efficiency, charge transport performance) and dark current (e.g., amount of dark time carrier) but also a governing factor for the signal responsivity, though this is scarcely mentioned in past reports. In use as a solid-state imaging device, all of high photoelectric conversion efficiency, low dark current and high response speed need to be satisfied, but there has not been specifically disclosed what an organic photoelectric conversion material or a device structure satisfies this requirement.
A photoelectric conversion film containing fullerenes is described in Patent Document 3, but only by fullerenes, it is impossible to satisfy all of the above-described high photoelectric conversion efficiency, low dark current and high response speed. Also, a solar cell using a bulk heterojunction film by a plurality of organic semiconductors, with at least one organic semiconductor being a crystal grain, is described in Patent Document 4, where, however, disclosure on the dark current and high-speed response is not found and application or the like to a photoelectric conversion device for imaging devices is neither described nor suggested.
In addition, conventional photoelectric conversion materials when heated sometimes cause sensitivity reduction or increase of the dark current and have room for more improvement in view of heat resistance.
[Patent Document 1] U.S. Pat. No. 5,965,875
[Patent Document 2] JP-A-2003-332551 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)
[Patent Document 3] JP-A-2007-123707
[Patent Document 4] JP-A-2002-076391